- Haskell-Cafe - Haskell.org

State monad exit
by p75213＠gmail.com 08 Apr '17

08 Apr '17

Hi, I am playing around with the State monad and queues. At the moment I have the following code: {-# LANGUAGE ViewPatterns, FlexibleContexts #-} module Main where import Criterion.Main import Control.Monad.State.Lazy import Data.Maybe (fromJust) import Data.Sequence ((<|), ViewR ((:>))) import qualified Data.Sequence as S -------------------------------------------------------- data Queue a = Queue { enqueue :: [a], dequeue :: [a] } deriving (Eq, Show) -- adds an item push :: a -> Queue a -> Queue a push a q = Queue (a:enqueue q) (dequeue q) pop :: Queue a -> Maybe (a, Queue a) pop q = if null (dequeue q) then go $ Queue [] (reverse (enqueue q)) else go q where go (Queue _ []) = Nothing go (Queue en (x:de)) = Just (x, Queue en de) queueTst :: Int -> Queue Int -> Queue Int queueTst 0 q = q queueTst n q | even n = queueTst (n - 1) (push (100 + n) q) | otherwise = queueTst (n - 1) (if popped == Nothing then q else snd (fromJust popped)) where popped = pop q ------------------------------------------------------------- pushS :: a -> S.Seq a -> S.Seq a pushS a s = a <| s pushS' :: a -> State (S.Seq a) (Maybe a) pushS' a = do s <- get put (a <| s) return Nothing pushS'' :: a -> State (S.Seq a) (Maybe a) pushS'' a = get >>= (\g -> put (a <| g)) >> return Nothing popS :: S.Seq a -> Maybe (a, S.Seq a) popS (S.viewr -> S.EmptyR) = Nothing popS (S.viewr -> s:>r) = Just (r,s) popS' :: State (S.Seq a) (Maybe a) popS' = do se <- get let sl = popS'' se put $ snd sl return $ fst sl where popS'' (S.viewr -> S.EmptyR) = (Nothing, S.empty) popS'' (S.viewr -> beg:>r) = (Just r, beg) queueTstS :: Int -> S.Seq Int -> S.Seq Int queueTstS 0 s = s queueTstS n s | even n = queueTstS (n - 1) (pushS (100 + n) s) | otherwise = queueTstS (n - 1) (if popped == Nothing then s else snd (fromJust popped)) where popped = popS s queueTstST :: Int -> State (S.Seq Int) (Maybe Int) queueTstST n = if (n > 0) then if even n then pushS' (100 + n) >> queueTstST (n - 1) else popS' >> queueTstST (n - 1) else return Nothing main1 :: IO () main1 = defaultMain [ bench "Twin Queue" $ whnf (queueTst 550) (Queue [500,499..1] []) , bench "Sequence Queue" $ whnf (queueTstS 550) (S.fromList [500,499..1]) , bench "State Queue" $ whnf (runState (queueTstST 550)) (S.fromList [500,499..1]) ] -------------------------------------------------------------------------------------------------------------------------------------------------- In the function "queueTstST" is there a way to exit while retaining the last "Maybe value" rather than with "Nothing"?

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LambdaConf standard registration opens
by Salas Sanchez-Bennasar 07 Apr '17

07 Apr '17

http://lambdaconf.us/events/2017/lcusc.html LambdaConf is one of the largest functional programming conferences in the world, focused on foundational concepts (such as lambda calculus, type theory, category theory), functional programming languages (Haskell, Scala, PureScript, F#, Clojure, Elixir, and more), new languages and approaches in functional programming, functional programming libraries, and related areas such as dependent types, proof systems, parallel array programming, functional GPU processing, and more. Standard registration is now open at Eventbrite: https://www.eventbrite.com/e/lambdaconf-2017-registration-29839799644 A complete list of sessions is online, including the following highlights: * 6 keynotes, including one on using Haskell to model life on the blockchain, one on how programmers brains work, and one on the axes of abstraction; * 8 leap workshops, including an in-depth workshop on category theory, one on optics, and one on building front-ends using PureScript Halogen; * 12 hop workshops, including one introducing Coq, another diving into recursion schemes, and another teaching functional data processing; * 9 de novo sessions, including on one formally specified digital logic, one on algebraic and monadic composability for distributed computing, and one on type-level REST programming; * 21 educational sessions, including one on Free monads, one on high-performance Haskell, one on codata and corecursion, one on FP on Android using Frege, and another on dependently-typed programming in Haskell; * 21 inspire sessions, including one on dependent-pairs, one on generative design, and one on type singletons. This is more than 110 hours of content, with enough variety and difficulty level for everyone. Speakers are book authors, contributors to open source libraries, researchers, and practicing functional programmers. The conference takes place in Boulder, Colorado, from May 25 - 27, at the University of Colorado Boulder in the foothills of the Rocky Mountains. Conference registration includes all sessions (including workshops), locally-catered breakfast and lunch on Thursday, Friday, and Saturday; a conference dinner on Friday night; a choice from a variety of networking activities on Sunday; free childcare and STEM workshops for children; all-gender restrooms and handicapped-accessible venues. Videos from some previous events can be found here: https://www.youtube.com/ channel/UCEtohQeDqMSebi2yvLMUItg; and here: https://www.youtube.com/ watch?v=JxC1ExlLjgw&list=PLE7tQUdRKcybh21_zOg8_y4f2oMKDHpUS The conference is preceded by commercial training opportunities on Monday - Tuesday, including: * Up & Running with Elixir & Phoenix, by Brooklyn Zelenka * Applied Haskell, by Michael Snoyman * Advanced FP in Scala, by John A. De Goes * Introduction to FP, by David Koontz * Mastering Apache Spark, by Pawel Szulc * Mastering Elm, by Isaac Shapira On Wednesday, several free mini-conferences are co-located with LambdaConf: * PureScript Conf 2017 * Introduction to FP with Haskell For more information on LambdaConf, the commercial training workshops, or the mini-conferences, please visit the website: http://lambdaconf.us/events/2017/lcusc.html

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Downsides of the Prompt Monad
by Michael Litchard 07 Apr '17

07 Apr '17

Could someone outline for me the downsides of using the Prompt monad?

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[ANN] etc-0.0.0 Declarative configuration spec for Haskell projects
by Román González 07 Apr '17

07 Apr '17

Is my pleasure to announce a new library for managing configuration values on Haskell projects. Some features: * Have a versioned spec of all values your application can accept * Provides an API for gathering values from multiple sources (files, overwrite files, cli arguments, environment variables) and then composing them into a single configuration map * Gives a sane precedence over sources of the configuration value sources * Provides inspection utilities to understand why the configuration is the way it is * Provides an API that abstracts away the source of configuration values and allows easy casting into record types your application or other libraries understand * Supports both configuration files in JSON or YAML (when cabal flags are used) * Dynamically generates CLI inputs from spec configuration file Any feedback, or comments feel free to create a ticket or send me a tweet over at @romanandreg Cheers. Roman Gonzalez.-

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Re: [Haskell-cafe] What is a safe Haskell data type to store and manipulate Money values
by Doug McIlroy 07 Apr '17

07 Apr '17

> REFERENCES TO LITERATURE PLEASE Another domain with pertinent literature is proportional representation in legislative bodies. Sorry, I have no particular references to offer. Doug

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Package maintainership takeover: quickcheck-instances
by Oleg Grenrus 07 Apr '17

07 Apr '17

The quickcheck-instances provides QuickCheck type-classes' instances for Haskell Platform packages. Unfortunately, author and current maintainer Antoine Latter is quite unresponsive. There is handful of PR open [2], and I had to use Hackage Trustee powers to allow new versions of dependencies (to keep e.g. Stackage nightly going on). I have tried to contact him to offer a co-maintainership help (at 14.12.2016). Cheers, Oleg Grenrus - [1]: http://hackage.haskell.org/package/quickcheck-instances - [2]: https://github.com/aslatter/qc-instances/pulls

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What is a safe Haskell data type to store and manipulate Money values?
by Sandeep Cr 06 Apr '17

06 Apr '17

Hello all, What is a good data type for storing and manipulating monetary values in a typical web application with payment processing? What are the pros and cons of various options like Data.Scientific, Rational and Decimal?

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Re: [Haskell-cafe] [Haskell] Haskell Tools
by amindfv＠gmail.com 06 Apr '17

06 Apr '17

Moving this conversation to haskell-cafe! > El 6 abr 2017, a las 04:15, Boldizsár Németh <nboldi(a)caesar.elte.hu> escribió: > > Thanks for asking, I just added a note that you need to install the haskell-tools-daemon package to use the Atom plugin for Haskell Tools. > > If you want to run refactorings from a script or just without an editor, you can use haskell-tools-cli as well. > >> On 2017.04.06. 10:40, Ivan Lazar Miljenovic wrote: >> Is there support for anything except Atom at this time? >> >> I'm also unsure of what I need to install on my local machine if I >> want to try it out (do I need the daemon? or is the cli tool >> sufficient?). >> >>> On 6 April 2017 at 17:03, Boldizsár Németh <nboldi(a)caesar.elte.hu> wrote: >>> Dear Haskellers, >>> >>> I'm happy to announce a new tool for refactoring Haskell source code. >>> Check it out: http://haskelltools.org/ >>> >>> Best Regards, >>> Boldizsár Németh >>> _______________________________________________ >>> Haskell mailing list >>> Haskell(a)haskell.org >>> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell > > _______________________________________________ > Haskell mailing list > Haskell(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell

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Re: [Haskell-cafe] [ANN] etc-0.0.0 Declarative configuration spec for Haskell projects
by Geraldus 06 Apr '17

06 Apr '17

Román González: > Was too excited delivering the newspaper that I forgot to add it to the > email: > > Github repo: https://github.com/roman/Haskell-etc >

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2nd call for papers: Trends in Functional Programming, 19-21 june 2017, University of Kent, Canterbury
by Peter Achten 05 Apr '17

05 Apr '17

----------------------------- C A L L F O R P A P E R S ----------------------------- ======== TFP 2017 =========== 18th Symposium on Trends in Functional Programming 19-21 June, 2017 University of Kent, Canterbury https://www.cs.kent.ac.uk/events/tfp17/index.html The symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions (see below). Authors of draft papers will be invited to submit revised papers based on the feedback receive at the symposium. A post-symposium refereeing process will then select a subset of these articles for formal publication. TFP 2017 will be the main event of a pair of functional programming events. TFP 2017 will be accompanied by the International Workshop on Trends in Functional Programming in Education (TFPIE), which will take place on 22 June. The TFP symposium is the heir of the successful series of Scottish Functional Programming Workshops. Previous TFP symposia were held in * Edinburgh (Scotland) in 2003; * Munich (Germany) in 2004; * Tallinn (Estonia) in 2005; * Nottingham (UK) in 2006; * New York (USA) in 2007; * Nijmegen (The Netherlands) in 2008; * Komarno (Slovakia) in 2009; * Oklahoma (USA) in 2010; * Madrid (Spain) in 2011; * St. Andrews (UK) in 2012; * Provo (Utah, USA) in 2013; * Soesterberg (The Netherlands) in 2014; * Inria Sophia-Antipolis (France) in 2015; * and Maryland (USA) in 2016. For further general information about TFP please see the TFP homepage. (http://www.tifp.org/) == SCOPE == The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: Research Articles: leading-edge, previously unpublished research work Position Articles: on what new trends should or should not be Project Articles: descriptions of recently started new projects Evaluation Articles: what lessons can be drawn from a finished project Overview Articles: summarizing work with respect to a trendy subject Articles must be original and not simultaneously submitted for publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Topics suitable for the symposium include, but are not limited to: Functional programming and multicore/manycore computing Functional programming in the cloud High performance functional computing Extra-functional (behavioural) properties of functional programs Dependently typed functional programming Validation and verification of functional programs Debugging and profiling for functional languages Functional programming in different application areas: security, mobility, telecommunications applications, embedded systems, global computing, grids, etc. Interoperability with imperative programming languages Novel memory management techniques Program analysis and transformation techniques Empirical performance studies Abstract/virtual machines and compilers for functional languages (Embedded) domain specific languages New implementation strategies Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2017 program chairs, Scott Owens and Meng Wang. == BEST PAPER AWARDS == To reward excellent contributions, TFP awards a prize for the best paper accepted for the formal proceedings. TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A student paper is one for which the authors state that the paper is mainly the work of students, the students are listed as first authors, and a student would present the paper. A prize for the best student paper is awarded each year. In both cases, it is the PC of TFP that awards the prize. In case the best paper happens to be a student paper, that paper will then receive both prizes. == PAPER SUBMISSIONS == Acceptance of articles for presentation at the symposium is based on a lightweight peer review process of extended abstracts (4 to 10 pages in length) or full papers (20 pages). The submission must clearly indicate which category it belongs to: research, position, project, evaluation, or overview paper. It should also indicate which authors are research students, and whether the main author(s) are students. A draft paper for which ALL authors are students will receive additional feedback by one of the PC members shortly after the symposium has taken place. We use EasyChair for the refereeing process. Papers must be submitted at: https://easychair.org/conferences/?conf=tfp17 Papers must be written in English, and written using the LNCS style. For more information about formatting please consult the Springer LNCS web site: http://www.springer.com/computer/lncs?SGWID=0-164-6-793341-0 == INVITED SPEAKERS == Conor McBride University of Strathclyde (UK) Cătălin Hriţcu INRIA Paris (FR) == IMPORTANT DATES == Submission of draft papers: 5 May, 2017 Notification: 12 May, 2017 Registration: 11 June, 2017 TFP Symposium: 19-21 June, 2017 Student papers feedback: 29 June, 2017 Submission for formal review: 2 August, 2017 Notification of acceptance: 3 November, 2017 Camera ready paper: 2 December, 2017 == PROGRAM COMMITTEE == Co-Chairs Meng Wang University of Kent (UK) Scott Owens University of Kent (UK) PC Jeremy Yallop University of Cambridge (UK) Nicolas Wu University of Bristol (UK) Laura Castro University of A Coruña (ES) Gabriel Scherer Northeastern University (US) Edwin Brady University of St Andrews (UK) Janis Voigtländer Radboud University Nijmegen (NL) Peter Achten Radboud University Nijmegen (NL) Tom Schrijvers KU Leuven (BE) Matthew Fluet Rochester Institute of Technology (US) Mauro Jaskelioff CIFASIS/Universidad Nacional de Rosario (AG) Patricia Johann Appalachian State University (US) Bruno Oliveira The University of Hong Kong (HK) Rita Loogen Philipps-Universität Marburg (GE) David Van Horn University of Marylan (US) Soichiro Hidaka Hosei University (JP) Michał Pałka Chalmers University of Technology (SE) Sandrine Blazy University of Rennes 1 - IRISA (FR)

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